I would agree with Nolatom. Stay on the preferred tack as long as possible, and if there's current (or a tidal stream) keep it in the lee, as that will give you a lift to windward.
Tacking effectively will not loose too much speed, but don't do it too often..
If you can anticipate a windshift, plan accordingly, as that may shorten the actual distance - sometimes you will get it wrong, though

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